Systems for controlling speed, torque and/or position of DC motors are known and have been widely used in a variety of applications including automotive control systems. Generally, such DC motors fall into two broad categories; namely brushed DC motors and brushless DC motors. While brushless DC motors typically offer desirable performance features and certain advantages over brushed DC motors in an automotive environment, such features and advantages may often be offset by the complexity of motor control and motor drive circuits required to accurately control motor operation. For example, controlled stoppage, accurate motor shaft positioning, motor reversal and consistent control of motor output torque are all difficult to achieve with brushless DC motors.
Dedicated systems for controlling and driving brushless DC motors are known. In such systems, a motor control circuit is typically operable to detect motor shaft position as well as motor drive current, and a motor drive circuit is, in turn, responsive to motor control signals supplied by the motor control circuitry to drive the DC motor in a desired manner. In known DC motor drive circuits, the motor control circuit typically includes a number of motor position sensors for providing a corresponding number of signals indicative of motor position as well as a sense amplifier operable to amplify one or more signals corresponding to motor drive current. The motor control circuit is typically responsive to motor position and/or motor drive current to provide the motor control signals to the motor drive circuit. Generally, the resolution of the motor control circuit is dependent upon the performance of the sense amplifier as well as the accuracy of the motor position detection circuitry.
Heretofore, many configurations of analog sense amplifiers have been designed, and some such configurations have been widely used in motor control circuits. However, such sense amplifier circuits suffer from several drawbacks, particularly when used in high voltage automotive applications. For example, known sense amplifiers developed for automotive applications often suffer from slow response time and high power dissipation. Moreover, due to high DC gains required in motor control circuit applications, most known sense amplifier circuits exhibit unacceptably high DC offset voltages, thereby resulting in a reduction of available system bandwidth. What is therefore needed is an improved sense amplifier circuit particularly suited for motor control system applications that is both power efficient and capable of high speed operation in a high voltage automotive environment